Building from Scratch or follow some plans?

[routercnc]

Hi Monk,

Firstly a quick check on Irving's first calc from the calalogue giving 0.00084mm deflection per Newton. I think this value is OK, as I'll show below.

1. For simplicity work out the equivalent RHS:
size Ixx Iyy
Profile: 40x80 614000 170000
RHS: 40x80x3 558332 208049
RHS: 40x80x3.5 636869 184292

Choose 40x80x3 to be on the safe side

2. Vertical bending, and deflection due to twisting:

20kg z axis (router, motor, metal brkts etc.)
length 1200mm
150mm to tool
40x80x3 alum RHS

Z bending deflection is 0.183mm (Irving got 0.164mm for 20kg using catalogue profile data, so think Irving's calc is OK)
X bending deflection is 0.028mm
twisting deflection is 0.003mm

3. You have an 'L' which is part way between the following results:
40x120x3 Z bending is 0.06mm, X bending is 0.020mm, twisting is 0.0019mm
80x120x3 Z bending is 0.043mm, X bending is 0.004mm, twisting is 0.0005mm

I need to create a spreadsheet to work out the true value, but it is between these. For a wood router it's looking OK to me.

If your z axis is less then 20kg, then you can ratio the Z bending deflection down accordingly (but not the twisting, or X bending).

If you go for just 80x80 profile:
Z bending 0.112mm
X bending 0.006mm
twisting 0.001mm

So you are better with what you have. Make sure they are well joined to each other, otherwise you will get back much less than this as they will work on their own.

4. Final note:
If you stack the profiles to get 40x160:
Z bending 0.031mm
X bending 0.015mm
twisting 0.001mm
which is the best of the lot (in bringing down the highest value) for no weight gain

You also asked about ballscrew location etc. I'll get back to you . . .

EDIT: added X bending results for completeness